NK cells (Natural Killer cells)

Natural Killer cells are innate lymphoid cells that eliminate virus-infected and malignant cells without prior antigen sensitisation, governed by a balance of activating receptors (NKG2D, NKp46, DNAM-1) and inhibitory receptors that recognise self-MHC class I molecules. NK cells also regulate adaptive immunity through rapid cytokine secretion, particularly IFN-γ. With aging, NK cell numbers in peripheral blood tend to increase but the cells shift toward a terminally differentiated, less proliferative phenotype with reduced cytotoxic capacity per cell and impaired cytokine production. This functional decline contributes to reduced tumour immunosurveillance and poorer control of herpesvirus reactivation in older adults.